I wanted this main tree to be really nice, and therefore I have spent most of my time creating it. The first thing was that I took a pencil and drew the tree in a way I wanted it to look in the scene. Than I scanned the picture in, took it to Max, placed it on a plane object and then place it in the scene where I wanted the tree to be. This sketch worked as a blueprint for me - but not for the front and side view, but only for the camera view! Generally speaking, I modelled this tree, so that it looked like the tree on the sketch. During the modelling I used two viewports - perspective and camera view.
While creating the texture, I had first spent a few hours searching for interesting shots and nice details of trees, which I could use for the texture. By doing this I found very nice textures, from which I chose the most beautiful one.
As you can see there are two kinds of moss and two kinds of bark. I find that getting a few references images makes the job of painting the texture so much easier. Here are the textures also with the unwrap.